There are numerous applications for lightweight head-worn near-to-eye displays. These are commonly called Head Mounted Displays (HMD). HMDs display to the eye an electronically rendered image such that the wearer perceives that they are watching a sizeable electronic display at some distance in front of them. The applications that use such HMDs are numerous, including but not limited to virtual reality, electronic gaming, simulation environments such as for military simulations or flight simulators, medical applications such as for the enhancement of sight, and consumer applications such as the ability to view videos in a mobile setting.
One of the fundamental challenges of HMDs is the tradeoff between the display's Field of View (FOV), being the size of the virtual display as perceived by the wearer, and pixel size. FOV is normally defined as the number of angular degrees subtended within the viewer's overall field of vision, horizontally, vertically, or on the diagonal. Horizontal FOV dimensions in the range of 20-30 degrees are typical, with larger dimensions being possible at significant expense. Pixel size is similarly expressed as the number of angular arc minutes ( 1/60th of a degree) subtended by a single, typically square pixel element. As one might expect, to achieve a larger FOV with a given pixel resolution (number of pixels), results in a larger pixel size, and consequent loss of image detail.
Peripheral vision is that portion of the human field of vision outside the center, say, 10-15 degrees FOV. Peripheral vision is extremely important in some HMD applications, especially those in which the wearer must maintain a connection with their natural environment to contextualize their situation, and enable way finding, orientation, and mobility. To provide significant peripheral vision via the electronic display requires an extremely large (and expensive) HMD. Alternately HMDs which provide a significant natural peripheral vision external to the HMD housing, provide a very limited virtual electronic FOV.
Many HMD applications can benefit from the incorporation of a live camera into the HMD, such that the wearer can not only view electronic data from a source, such as a video file, but also live video images of the world in front of them. Image processing can be used to enhance the live camera image before it is presented to the eye, providing magnification, enhancement of brightness, or improved contrast for example.
In HMD systems that are to be used for multiple activities, different camera angles may be required for different tasks. For example, to observe an object a distance, the camera angle should be nearly horizontal relative to the horizon when the wearer's neck is straight and their gaze angled at the horizon. On the other hand, to view hand-held objects at a close distance requires a camera that is angled downward, in order to avoid a highly exaggerated downward neck posture. In this manner, the angle of the camera mimics the angular movement of one's eyes in a non-HMD world.
Finally, the angle of the display relative to the eyes is also dependent on the specific tasks of the wearer. In certain situations the wearer would like to look into the electronic display only temporarily, and by looking up at an angle higher than their habitual gaze. In other situations, the wearer would prefer a more immersive usage model, where the electronic display is directly in front of their normal line of gaze.
What is needed then is a general HMD device that is capable of providing significant unobstructed peripheral vision outside of the electronic display FOV, while simultaneously providing a high resolution video image. Further, the ability to adjust the angle of the display and the camera according to the wearer's specific activity would provide significant comfort and increased usability.